Various types of ion sources may be used to create the ions that are used in semiconductor processing equipment. For example, an indirectly heated cathode (IHC) ion source operates by supplying a current to a filament disposed behind a cathode. The filament emits thermionic electrons, which are accelerated toward and heat the cathode, in turn causing the cathode to emit electrons into the arc chamber of the ion source. The cathode is disposed at one end of an arc chamber. A repeller is typically disposed on the end of the arc chamber opposite the cathode. The cathode and repeller may be biased so as to repel the electrons, directing them back toward the center of the arc chamber. In some embodiments, a magnetic field is used to further confine the electrons within the arc chamber.
In certain embodiments, electrodes are also disposed on one or more side walls of the arc chamber. These electrodes may be positively or negatively biased so as to control the position of ions and electrons, so as to increase the ion density near the center of the arc chamber. An extraction aperture is disposed along another side, proximate the center of the arc chamber, through which the ions may be extracted.
In certain embodiments, it may be desirable to utilize a feed material that is in solid form as a dopant species. However, there are issues associated with using solid feed materials with IHC ion sources. For example, vaporizers used with ion sources are difficult to operate at temperatures greater than 1200 Celsius. Further, there may be issues with heat shielding and condensation in the tubes that connect the vaporizer with the arc chamber. These issues may prevent the use of many solids in a vaporizer because their vapor pressure is too low at 1200 Celsius.
Therefore, an ion source that may be used with a solid feed material without these limitations would be beneficial. Further, it would be advantageous if the ion source was not contaminated by the solid feed material.